1. Technical Field
The present invention relates to a method of reducing the viscosity and/or overall molecular weight of viscosified fluids to a desired value in subsurface hydraulic fracturing through the administration of a time delayed breaker composition.
More specifically, the present invention describes a method and composition for reducing the viscosity and/or overall molecular weight of viscosified fluids to a desired value in subsurface hydraulic fracturing through the administration of a time delayed breaker composition including water, a peroxygen, a peroxygen inhibitor, and a peroxygen activator.
2. Background Art
Hydraulic fracturing is a well-stimulation technique in which subsurface rock formations are fractured by the introduction of a hydraulically pressurized liquid. As a result of the cracks or fractures that are formed in rock formations, natural gas and/or petroleum flow and extraction from a well may be increased. Additional solid material additive components, commonly referred to as hydraulic fracturing proppants, may also be added to the hydraulic fracturing fluid to hold the fractures open.
Various form of hydraulically pressurized liquid are currently used, including viscosified fluids such as slick water, linear gels and cross-linked gels. While such viscous fluids are capable of carrying more concentrated proppant into subsurface rock formations, these viscofied fluids do present various drawbacks. One shortcoming regarding the use of viscosified fluids for stimulation and fracturing applications is the difficulty in effectively removing or extracting the viscofied fluid from the formation without removing the proppant from the fractures. Prior attempts to remove the viscosified hydraulic fracturing fluids have included the introduction of chemicals to reduce the viscosity of the fracturing fluids, commonly known as breakers. Examples of such break systems include the use of oxidative chemistries in various forms, as well as other methods that utilize chelants, surfactants, etc. However, many of these oxidative breaker systems do not achieve the desired degree of reduction in fluid viscosity and/or the desired degree of reduction in polymer molecular weight. Additionally, many of these prior oxidative breaker systems cannot perform the desired reduction in fluid viscosity and/or the desired reduction in polymer molecular weight in a delayed manner.
In order to increase the efficiency of oxidants used for breaking viscosified fluids various catalytic agents have been employed for the purposes of decreasing reaction time and free radical generation.
Despite these advancements, it is still desirable to overcome these shortcomings to reduce the viscosity of such viscosified hydraulic fluids and/or reduce the molecular weight of the water soluble polymers within such fluids to desired levels within a specific timeframe in which the fluids can be both pumped down hole and the formation stimulation completed.